It is often desirable to use high frequency switchmode battery chargers in telecommunications applications. Such battery chargers typically include a transformer for stepping an ac source voltage to an appropriate level, and a rectifying circuit for converting the power signal on the secondary side of the transformer to direct current. The rectifying circuits in these chargers typically employ diodes for rectification.
Schottky diodes have certain inherent characteristics that make those devices attractive for rectification applications. For example, Schottky diodes typically exhibit a low forward voltage drop and a fast reverse recovery time. The low forward drop characteristic would be advantageous in a rectification circuit for a battery charger or the like as the circuit would typically enjoy a greater power throughput. The fast reverse recovery characteristic would also be advantageous in high frequency switchmode chargers from a power throughput perspective.
Unfortunately, many telecommunications applications require significant output voltages; often on the order of 48 volts dc. The limited peak inverse voltage characteristic of Schottky diodes has, in the past, typically precluded their use in rectification circuits operating at such voltage levels.
Some prior art approaches to rectification in high frequency switchmode battery chargers have employed rectification circuits using inductors and diodes on the secondary side of a center-tapped transformer. These approaches have suffered from certain disadvantages. For example, the center-tap approach produces a half-cycle secondary current. Thus, such approaches do not utilize the transformer efficiently, and require a larger, and typically more expensive, transformer to produce a secondary current at a level near that produced by a smaller transformer producing a full wave secondary current.